For filling:
Using electric mixer, beat cream cheese, sugar, lemonade concentrate and lemon zest in large bowl until smooth. Beat in 3/4 cup sour cream. Add eggs 1 at a time, beating just until combined. Pour filling into crust. Bake until center moves only slightly when pan is shaken, about 50 minutes. Transfer cake to rack; cool 5 minutes.

Meanwhile for topping:
Whisk 1 cup sour cream in small bowl until very smooth. Whisk lemon curd in another small bowl until very smooth.

Run small sharp knife around sides of cake. Starting at outside of edge of cake, spoon small alternating dollops of sour cream and lemon curd side by side in concentric circles atop warm cake, covering cake completely. Gently shake pan to smooth out toppings. Using tip of knife, gently swirl toppings, forming marble design. Chill cake uncovered overnight.

Run small sharp knife around sides of cake to loosen. Release pan sides of cake to loosen. Release pan sides. Transfer cake to platter. Garnish with lemon slices and mint sprigs.